The difference between 싶어 하다 and 싶어지다?

Question

What is the difference between 싶어 하다 and 싶어지다? The dictionary says that both means want to ~ and should be used as a form of 고 싶어지다. Or to make an example:

누가 얘기하고 싶어 해요.

In this sentence, can I just change it to 싶어지다 and is it interchangeable?

Answer 1

싶어지다 means to start to want something. In general, -어지다 after an adjective (형용사) means to change the state to be (something).

E.g.,

물이 뜨겁다. The water is hot.

물이 뜨거워졌다. The water got hot.

물이 뜨거워진다. The water is getting hot.

배가 고프다. I'm hungry

라면을 보니 배가 고파졌다. I got hungry at the sight of ramen.

라면(이/을) 먹고 싶다. I want to eat ramen.

라면(이/을) 먹고 싶었다. I wanted to eat ramen. (I probably don't now.)

라면(이/을) 먹고 싶어졌다. ~ I didn't, but now I want to eat ramen.

라면(이/을) 먹고 싶어졌었다. (rare) ~ I hadn't, but then I wanted to eat ramen. (I probably don't now.)

In addition, 싶다 and most(?) other feeling-related adjectives usually take -하다 for 2nd/3rd person (except for 2nd person questions). Using 기쁘다 be happy as an example:

친구가 와서 기쁘다. I'm glad that (my) friend came.

친구가 와서 기쁘니? Are you glad that (your) friend came?

너 어제 친구가 왔다고 무척 기쁘더라. (X)

너 어제 친구가 왔다고 무척 기뻐하더라. (O) You looked so glad yesterday that your friend came.

철수가 어제 친구가 왔다고 무척 기쁘더라. (X)

철수가 어제 친구가 왔다고 무척 기뻐하더라. (O) Chulsoo looked so glad yesterday that his friend came.

철수는 어제 친구가 와서 무척 기뻤다. Chulsoo was so glad yesterday that his friend came. (This kind of form is used only in a story, where the narrator can see inside Chulsoo's mind. It can't be used if you're talking about your real friend Chulsoo.)

So, answering your question, 누가 얘기하고 싶어져요 is impossible, because (1) 누가 is third person and (2) -져요 means someone is beginning to feel that they want to talk, which is rather weird in this context.

However, you could say, e.g., 그 영화를 보고 너와 얘기하고 싶어졌어 After seeing the movie, I want to talk to you. (Or, The movie made me want to talk to you.)

Answer 2

'-지다 (in the form of -어지다)' is an auxiliary verb (보조동사) which is used to mean:

남의 힘에 의하여 앞말이 뜻하는 행동을 입음을 나타내는 말. (Literally) An action is done to a persons or thing because of other person's action or force.

약속 시간이 1시간 늦춰졌다 (늦추어졌다). The appointment (time) has been postponed for an hour (by somebody).

새로운 말들이 만들어지다. New words are made (by people).

It is closer to the passive voice in English. However, it has another function:

앞말이 뜻하는 대로 하게 됨을 나타내는 말. (Literally) A person is made to do as if the meaning of the preceding word dictates. (It's not easy to understand unless you read examples.)

그 사람의 말이 사실인 것처럼 믿어진다. I am made to believe as if what he said were true. (His words could be true or not, but his words make me believe what he says.)

'싶어지다' could be used in the following example:

(다이어트 중인데도) 음식을 봤을 때 먹고 싶어졌다. (Even though I was on a diet) When I saw the food, I was made to feel like eating (Literally).

In other words, the food made me feel like eating the food.

'싶어 하다' is completely different. It is rather active than passive. In order to understand this phrase, you should know what '싶다' means:

[Auxiliary adjective] 앞말이 뜻하는 행동을 하고자 하는 마음이나 욕구를 갖고 있음을 나타내는 말. (Literally) A word that indicates you have willingness or desire to do what the preceding word means.

먹고 싶다. I have desire to eat (I want to eat). 보고 싶다. I have desire to see (I want to see).

You add '하다' to '싶어' indicate an action. For example:

누가 얘기하고 싶어 해요. (Literally) Somebody has the desire to talk. (Somebody wants to talk)

?누가 얘기하고 싶어요. It is not idiomatic as the subject is the third party.

You should put a space between "싶어" and "하다" unlike "싶어지다" which doesn't need a space.

A side note: Your question seems to be one of the most difficult questions posted on Korean SE. I am not a linguist and the above explanation is the best I can provide.